Evidence of Magnon-Mediated Orbital Magnetism in a Quasi-2D Topological Magnon Insulator.

We explore spin dynamics in Cu(1,3-bdc), a quasi-2D topological magnon insulator. The results show that the thermal evolution of the Landé g factor ( g ) is anisotropic: g in-plane decreases while g out-of-plane increases with increasing temperature T . Moreover, the anisotropy of the g factor (Δ g ) and the anisotropy of saturation magnetization (Δ M s ) are correlated below 4 K, but they diverge above 4 K. We show that the electronic orbital moment contributes to the g anisotropy at lower T , while the topological orbital moment induced by thermally excited spin chirality dictates the g anisotropy at higher T . Our work suggests an interplay among topology, spin chirality, and orbital magnetism in Cu(1,3-bdc).